1. Field of the Invention
Since the demonstration that a wide variety of genes expressing proteins from prokaryotes and eukaryotes could be introduced into foreign hosts and expressed, there have been continuing efforts to expand the capabilities and efficiencies with which the proteins can be produced and isolated. The efficiency with which a particular protein may be obtained will vary greatly depending on a wide variety of factors.
While the code for translating from RNA to amino acid is substantially universal, as a practical matter codons may be more or less efficiently translated depending upon the host. Depending upon the ratios of tRNAs, genes may be translated with varying efficiencies into the desired protein. To the extent that the host is more closely related to the source of the gene, it is anticipated that the gene will be more efficiently translated. Also, alien regulatory signals controlling the transcription and translation of the gene may be useful, avoiding the need to substitute the host regulatory signals for the regulatory signals of the gene source.
Also of interest is whether leader peptides will be recognized by the host to secrete the proteins of interest. Particularly desirable is where the leader peptide which is naturally present is recognized by the host, so that the need for introducing a synthetic leader is not required. However, the ability to obtain secretion of the desired peptide is not the most important factor and this will vary from host to host.
Also of interest is the nature of the products that the host or other species related to the host produces. In this situation, one can expect that by taking a gene from a related source and introducing it into an expression host, the product will be efficiently produced. Particularly for non-proteinaceous products where a useful host lacks only one or two enzymes in the metabolic sequence for production of the desired product, these enzymes could be introduced into the desired host to provide the desired product.
Another consideration is the ability to grow the host commercially, it being desirable that the same or similar host have been the previous subject of commercial fermentation processes.
2. Brief Description of the Prior Art
Stohl, et al., Nucleic Acids Res. (1982) 10: 1439-1458 describes the characterization of two plasmid DNAs found in mitochondria of wild-type Neurospora intermedia strains. Collins, et al., Cell (1981) 24:443-452 describes the characterization of a novel plasmid found in mitochondria N. crassa. Case, et al., PNAS USA (1979) 76:5259-5263 describes the efficient transformation of N. crassa by utilizing hybrid plasmid DNA. Hymen, et al., PNAS USA (1982) 79:1578-1582 and Zakian, ibid (1981) 78:3128-3132 describes the use of mitochondrial DNA for high-frequency transformation for yeast. Stahl, et al., PNAS USA (1982) 79:3641-3645 have reported experiments with Podospora employing a hybrid plasmid consisting of E. coli plasmid pBR325 and defective mtDNA expressing the senescence traits.